Apparatus for mixing signals are known in the electrical art. One use of such a mixing apparatus, referred to as a mixer, is to combine a modulated or modulating signal with a local oscillator signal to produce a further modulated signal at another frequency so that the further modulated signal may be broadcast or detected. In a typical wireless communication receiver application, a modulated radio frequency (RF) signal is combined in a mixer with a local oscillator (LO) signal to produce an intermediate frequency (IF) signal which may be then further amplified and detected to recover information that was modulated onto the RF signal. In a transmitter, the process is reversed so that the LO signal is mixed with the IF signal to produce an RF signal that is amplified and transmitted.
Although conventional mixers may be used to mix such signals, the mixing process performed by such conventional mixers has nonlinearities that typically produce undesirable spurious signals, such as unwanted third order intermodulation products of the input signals. It would therefore be desirable to provide an improved mixer with improved linearity that could reduce such spurious signals. In addition, it would be desirable if the improved mixer could be implemented using integrated circuits to provide an economical device. Accordingly, there exists a need for an improved mixer that reduces spurious signals and may be economically produced using integrated circuit technology.